A generalized frequency detuning method for multidegree-of-freedom oscillators with nonlinear stiffness

In this paper, we derive a frequency detuning method for multi-degree-of-freedom oscillators with nonlinear stiffness. This approach includes a matrix of detuning parameters, which are used to model the amplitude dependent variation in resonant frequencies for the system. As a result, we compare three different approximations for modeling the affect of the nonlinear stiffness on the linearized frequency of the system. In each case, the response of the primary resonances can be captured with the same level of accuracy. However, harmonic and subharmonic responses away from the primary response are captured with significant differences in accuracy. The detuning analysis is carried out using a normal form technique, and the analytical results are compared with numerical simulations of the response. Two examples are considered, the second of which is a two degree-of-freedom oscillator with cubic stiffnesses

Resonant response functions for nonlinear oscillators with polynomial type nonlinearities

In this paper we consider the steady-state response of forced, damped, weakly nonlinear oscillators with polynomial type nonlinearities. In particular we define general expressions that can be used to compute resonant response functions which define the steady-state constant amplitude oscillatory response at the primary resonance and the associated harmonics. The resonant response functions are derived using a normal form transformation which is carried out directly on the second-order nonlinear oscillator. The example of a forced van der Pol oscillator with an additional cubic stiffness nonlinearity is used to demonstrate how the general analysis can be applied